Aluminum alloys are used in a variety of applications where they will not be exposed to severe temperature environments. For example, certain of the alloys are extensively employed in light weight structures, such as are present in subsonic aircraft systems, because of their high strength to weight ratio, low cost and good formability. These high strength alloys, designated in the art as 7000 series alloys, contain as their principal components a major amount of aluminum and minor amounts of magnesium and zinc.
The high strength alloys are, however, restricted in their use because of their susceptibility to stress corrosion cracking. Improvement in stress corrosion resistance has been accomplished by conventional tempering procedures, but any increase has been gained at the expense of strength. Ostermann in Metallurgical Transactions, 2, 2897-2902 (Oct. 1971) describes a thermomechanical process for treating a series 7000 aluminum alloy whereby the strength properties of the alloy are substantially improved. However, the process disclosed by Ostermann does not result in any substantial increase in the resistance of the alloy to stress corrosion.
The principal object of this invention, therefore, is to provide a process for treating 7000 series aluminum alloys so as to increase materially their stress corrosion resistance without decreasing their strength properties to any substantial degree. Other objects and advantages of the invention will become apparent to those skilled in the art upon consideration of the accompanying disclosure.